Process for separating and refining impurities from lead bullion

ABSTRACT

The Razor Process™ is a unique pyrometallurgical lead refining process. Benefits from the Razor process™ include: lower energy costs; improved working environment; reduced recycling costs; increased refining productivity; reduced cycle time and labor requirements; and production of secondary recyclable products, therefore yielding unique and immediate benefits.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims a benefit of priority of provisional application No. 60/873,184, and entitled “Process for Separating and Refining Impurities from the Lead Bullion”, filed Dec. 5, 2006.

FIELD OF THE INVENTION

This invention relates to a unique lead refining process, impurity separation and removal.

BACKGROUND

The metallurgy of lead has been very well researched and developed from Roman times forward. Pyrometallurgical techniques were used in ancient England to refine lead and desired alloys, as disclosed in A Study of Lead Softening, Vineburg, Daryl Geoffrey, Master's Thesis. McGill University, Montreal, Canada (2003). The known art of refining advanced with the advent of the process patented by Henry Harris, et.al, in London, England ISD 1922, as disclosed in Harris Process, Jones, T. D., ASARCO, The Wisconsin Engineer Volume 33 Number VII (1929). The “Harris process” used slag composition manipulation during pyrometallurgical processing to selectively remove impure compounds and elements found in lead bullion. The “Harris process” provides an environment where the lead impurities consisting of antimony, arsenic, tin, tellurium, and selenium are oxidized out of the lead by mixing or otherwise contacting the molten lead bullion with mildly oxidizing slags consisting of alkali metal hydroxides and other salts. Utilizing the “Harris process,” the oxidizing power of the slag is then enhanced by use of air, or other oxidizing slags, such as alkali hydroxides mixed with alkali nitrates. After the alkali slag is sufficiently laden with impure metal hydroxides and compounds, the slag is decanted or otherwise removed from the lead.

By 1922, The American Smelting and Refining Company (“ASARCO”) had adapted the “Harris process” to use slag as a vehicle for initiating the refining operation at the ASARCO refinery at Perth Amboy, N.J. A Patent by Betterton, et.al, in 1932 detailed the use of chloride slag mixtures as the venue for impurity recovery from the refining of lead bullion. Betterton used addition of gaseous chlorine to the molten slag provided the oxidizing power to drive the impurity level in the slag to optimum levels. While not stated in the Betterton Patent, the volatility of the various chlorides, particularly arsenic trichloride made the requirement for a gas handling system imperative. Betterton adjusted the composition of the molten slag, consisting of NaCl, CaCl₂, MgCl₂, and KCl to produce a very low meting point. As the slag became loaded with impurity metal chlorides, the viscosity and melting point changed thus providing the operator with convenient control parameters.

More modern processes include the KIVCET process where slag oxidation/reduction control is accomplished in the furnace rather than in the refining kettles. As the 20^(th) century drew to a close, costs and environmental considerations changed the complexion of lead refining and alloy production.

Practically speaking, the only waste products that can be economically disposed to the environment are: very low lead content iron/lime/silica blast furnace slags that must pass the EPA TLCP test; very clean alkali salts such as chlorides, sulfates, or carbonates; and very limited amounts of sulfur dioxide (released to the atmosphere). In many cases the air discharge limits on SO₂ are so low that conversion to marketable commercial sulfate solution is necessary.

The United States secondary lead smelting industry is subject to environmental restrictions regarding discharge levels of lead and other toxic metals. Consequently the industry is forced to utilize reagents that have minimal impact on the discharge levels of toxics into the environment. One such reagent is air or oxygen. The use of air or oxygen for lead bullion refining has a very low initial cost. However, the process requires a very hot kettle (1000° F. to 1200° F.), which consumes fuel and shortens kettle life. The process is slow and the by-product lead oxide containing the antimony, tin, arsenic and other elements consumes eight to twelve percent of the lead in the kettle. Lead loss, added energy costs and shortened kettle life make the process expensive. In addition, tons of fluffy lead oxide powder forming on top of the refining kettle must be removed manually. This lead oxide by-product is an environmental threat and as such, is strictly regulated by the EPA and OSHA.

Current production processes and practices using air for kettle refining exhibit high energy cost, lead-in-air regulatory compliance issues, long processing times (more than eight hours), and a nominal ten percent loss of product to the recycle loop for every kettle treated.

This invention uniquely improves the traditional lead refining process and rectifies problems associated with impurity separation.

SUMMARY OF THE INVENTION

The Razor Process™ is a unique lead refining treatment whereby reagents are added to induce impurity separation. Benefits from the Razor Process™ include: lower energy costs; reduction or prevention of environmental contamination; reduced recycling costs; increased batch refining productivity; reduced time; reduced labor requirements; and production of secondary recyclable product.

DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a lead refining process.

DETAILED DESCRIPTION OF THE INVENTION

The Razor Process™ utilizes each of the following elements:

(1) The use of a Lewis Acids to remove impurities dissolved in lead bullion.

(2) Controlled use of compounds in the refining step cause impurities to behave as a Lewis Base.

(3) Separation occurs under (or in) a liquid slag layer well below the traditional temperature range of 900° F. to 1200° F. for traditional pyrometallurgical refining of lead.

(4) Upon reaction, the oxides of amphoteric p-block elements are converted to a more basic state.

(5) A prescribed amount of Lewis Acid is added to remove lighter amphoteric elements.

(6) The Razor Process™ creates uniquely low potential for reversible reaction at the temperatures involved, thus allowing for process flexibility and reuse of the molten slag until the level of amphoteric p-block element impurities reaches a concentration greater than 10% in the Razor Process™ Slag melt layer. At this concentration the melt is removed for subsequent processing.

(7) Solubility control of the metal salts and base metal prills is uniquely managed with an excess of free Arrhenius base mixture.

Minor adjustments to all or a portion of the Razor Process™ steps, as identified above, may be employed to accommodate individual plant operations.

The foregoing description explains the invention. 

1) A compound is added to lead bullion to react with amphoteric p-block elements to form Lewis bases. 2) Separation occurs at the liquid/liquid (or metal/slag) interface at a temperature less than 850° F. 3) The resulting Razor Process™ Slag layer, then incorporates the metal salts of amphoteric p-block elements. 4) The admixed amphoteric Lewis Acid is then reduced by the impurities removed from the lead bullion. 5) The precise stoichiometric amount of amphoteric Lewis Acid is added to preferentially remove the lighter amphoteric elements. 6) There is low potential for reversible reaction at the temperatures involved, thus allowing for process flexibility and reuse of the molten slag until the level of amphoteric p-block element impurities reaches a concentration greater than 10% in the Razor Process™ Slag melt layer. At this concentration the melt is removed and delivered to subsequent processing. 7) The entire Razor Process™ takes approximately six hours from start to finish, which is much less time than the traditional refining and separation processes, which typically takes approximately eighteen hours from start to finish. 